Draft tube structure



Feb. 14,1933. H. B. TAYLOR 1,897,501

DRAFT TUBE STRUCTURE Original Filed Jan. 14. 1922 4 Sheets-Sheet lTTORNEYJ Feb. 14, 1933. H. .B. TAYLOR 1,897,501

DRAFT TUBE STRUCTURE Original Filed Jan. 14, 1922 4 Sheets-Sheet 2 1 ByM/ Feb. 14, 1933. H. B. TAYLOR 1,897,501

7 DRAFT TUBTEI STRUCTURE Original. Filed Jan; 14. 1922 4 Sheets-Sheet 4IN VEN TOR 'ATTORNEYS Patented Feb. 14, 1933 rem I-IA-HVEY Bmonenn ryme, or PHILADELPHIA, PENNSYLVANIA YD'RAF'I "TUBE STFIUCTURE Application"filed ZFa'nu'aiy 14, "1522,Sriei1No. 529172. Renewed Maya, 1929.

This invention relates 'to a draft tube for-a hydraulic turbine andparticularly -'to a dra'ft tube or discharge passage in which the how'is' turned from the generally axial-"direction to a diree'tion atanangle thereto. In inaking-suchabencl, the design "of many existing 5tubes fails to tzike proper accounto'f all components of the velocity 1of discharge from a turbine runner. The result is "that\va-steiu'leddies and disturbances are-set up, r hichofte'n causeserious vibra ties of the Water column and frequently 01": the entirepowerhouse foundeltion and such "eddy fo11n'ation,'besi'de srepresenting a Waste ofenergy-andloss-of'ificiencyyniey in some'case'scause serious damage-to the structure through vibration anderosion. Inmany installations it has been necessary to redesign theentire draft'tube passages-or to adinit air 'to the discharge ii-om therunner "ilrorder {to reduce the shocks due "to the hydraulicdisturbance, but this introduction of air does not avoid wastefuldisturbances of the flow and by reducing the vacuum at theyrunnerdischarge further decreases the efiicie'nc-y of the'turbine.iii-manyinstallations theavail- 'ublespace Which-can be-occupiedbyJhedraiit cube is limited, particularly in n horizontal ndirectionmeasured lengthwise oi tlieipowe'n nae; being irequen'tlnecessary 'to make is dimension small to'pei'inite'close spacing ofsuccessive units and ashort total length of powerhouse.

object of the present invention is to Q overcome the objections to priorstructures 'and provide a draft tube adapted "to turn the flow atangles-to theax'ial'without e-X- ve'distiirbance andobs'truction'zind"Within n ni'ted lateral dimensions permitting a @1053 s pacing ofadjacent 'turb'ine units. In ipurciculirr, his invention comprises theforination within the bend of the draft tube of centred surfaces adapted"to give the passage in its portion near the beginning of the bendagenerally annular formation spreading the fiow'o' ardironi theaai's'andivhenapplied whirling fiow con fer 'ing to the lines of low which thestream lines tend to take "and JYGVQ? ting as far as possible thefor-mation watefu'l disturbances.

\ In the accompanying dravvings'illustrating the invention Fig.1is'a'-vertica1:setionalviewofa draft tube oPtheelbowtype With centralsurfaces formed in accord ance -With *this invention.

FigsJQ tO 14 are sectional'vievvs of modifiestions showing the*application of the invention "to diiierent forms of tube and variousconditions offlow.

Figs. 15 and IBare niOdified formsofthe draft tube, and

Fig. 17 is a sectional View on dine 17 17 o'f lT-i g. '15.

In the specific embodiment of the invention shoxvn in Fig. 1 a tu'rbineT'has a'n in take passage 5 leading throughvanes dtothe runner 7 "whichdischarges vertically dov'vnwa'rd into the draft tribe D ofelbow shape,receivingthe fiow verticall and discharging n horizontally {into thetailwa'ter T. 'The theft tu'be D is of :generally circular section inits entrance ortion and its bend has an inner curve at 8 andan'outer'curve at 9 turning'the'flo w'through spproximatly'sao. In Msuch a draft tube,-it has been found tha'tcross 5 currents anddisturbances are set up under practically all conditions of operation;and frequently it is found that in such tubes a portion ofthe passage isoccupied by Water flowin upWard toward the runner. The conditions insuch aftu'be are p'a'r ticula rly 'un favorable in turbines of highspecific speed in which the discharge from the runner at all gateopenings 'coi'itains la'rge "whirl "components of velocity about the"turbine axis. In some turbines of low specific speed, the're may beoperating conditions atapproximatelv normal gate in Whic'hthe dischargefrom the runner contains little Whirl about "the 0 axis, but even insuch installations there is 5J0 severe Whirl a't part gate and Wide-openga te, operation; and the Whirl set up in th'e'dra'it't tube under suchconditions may have serious consequences. This is particularly true whenthe turbine is supplied through a long pensftock in which Water hammer"or'surging may be set upbythe draft tube vibration.

When the flow entering the draft tube'contains large rotationalmotion'about the axis, there is a tendency for a space tobeleft'withinthe downward flowing stream in which the flow is frequently upwardtoward the runner and in which the conditions are unsteady. In thehorizontal portion of the draft tube, the flow is frequently outward onone side of the tube and reversed in direction on the other side.

To avoid this wasteful disturbance of the flow and the accompanying lossof power and efficiency, as well as danger to the power house structurethrough vibration, there is added in accordance with this invention acore C in the form of a cone withits apex 12 at or near the axis of thetube and its surfaces formed generally as surfaces of revolutionco-axial or nearly so with the entrance portion of the draft tube. Thesurfaces of the cone expand and curve downward to a base 14: resting onthe outer curve 9 of the draft tube elbow. This core C may be of metalor of concrete built up from the bottom of the elbow in the generaldirection of the turbine axis and extended upward any desired distance.The core, if of concrete, would contain proper reinforcement and wouldbe bonded to the surrounding structure by anchor rods or reinforcingrods such as is shown at s, Fig. 1. This reinforcement is necessary towithstand the tendency of the core to be drawn upward by the reductionof pressure in the draft tube.

The outflow through the draft tube is thus guided into annular formaround the central core C within the elbow and the core fills any voidthat may tend to form and provides central surfaces around which theflow may pass on naturally whirling lines to the lower horizontalportion 20 of the draft tube. The side 16 of the core has a longersurface than the opposite side 17 and may extend somewhat into thehorizontal discharge portion 20, while the corners 21 formed by themeeting of the core and tube surfaces are rounded off in smooth and evenmanner. In many existing tubes of the elbow type, the flow is not onlyturned sharply at the elbow, but the cross sectional areas of thepassage enlarge with undue rapidity in passing around the bend so thatthe flow does not fill the entire passage. The central core is of valuein reducing the excessive areas in such tubes and is of advantage whenused with nonwhirling flow, in addition to providing for the tangentialcomponents of flow when the flow is whirling.

In some cases it may be desirable to make the core C somewhatnon-circular in section in order to accommodate it to the areas of theparticular form of bend involved or it may be desirable to cut away orbuild up portions of the surrounding tube surfaces to give oesired formto the water passage around the cone.

In the modification shown in Fig. 2 the draft tube D instead of having acurved el bow turns the flow at right angles against a deflectingsurface 61 and collects the spread ing flow in the surrounding passage30 leading to tailwater at 31. Such a form of draft tube causes abruptchanges in velocity of the flow and has been found. in practice to setup serious vibrations of the water column. To overcome this objection inaccordance with this invention a central core C is shown built up on thedeflector surface d and extending into the draft tube D any desireddistance and forming the lower end of the draft tube into a spreadingannular passage. Preferably the surfaces of the central core C are sospaced with relation to the draft tube surfaces as to form a passagegradually increasing in area across the lines of flow so that throughoutthe draft tube there will be a substantially continuous deceleration ofthe flow and resultant conversion of velocity head into pressure head atthe outlet.

In the formation of the central core it is desirable to avoidobstruction of the flow as by sudden changes in velocity or direction.In some existing installations the shape of the outer wall may be suchthat the restriction caused by the central core may interrupt thedesired gradual enlargement of the cross section but the smoother flowlines and absence of vibration with the resulting increased efficiencyand reliability will more than olfset any loss due to the shortcontracted portion.

In the modification shown in Figs. 3 to 8 the draft tube elbow 35 beginsto curve toward the horizontal immediately at the runner discharge andits design is such as to provide an excessively large final outletpassage 36. The cone 37 built into this tube has its surface 38 carriedout into a flat floor 39 above the elevation of the original floor 40.As is clearly shown in Figs. 6 and 7 which are sectional views on lines66, 77 of Fig. 3, this reduces the cross sectional area of the outletpassage so as to avoid the formation of obstructive countercurrents andeddies. Fig. 5 is a sectional view on line 55 of 3 and shows theeccentric position occupied by the core 37 with relat on to the center41 of the portion of the passage in which it is set. This core ishowever shown as vertically concentric with the center of the entrance42 to the draft tube as shown in Fig. 4 which is a plan view with dottedlines l?) representing the extreme horizontal width of the tube atvarious sections. The initial portion of core 37 is shown as formed as asurface of revolution around a vertical axis.

This shape is however modified for instance to give the core surfaces agenerally spiral formation as indicated by lines 15 in Fig. 16 which isa sectional view on line 16-16 of Fig. 15. The rounded entrance edge ofthis spiral is shown by the line 45' A be symmetrical of Figs. and 17..This form of passage allows a greater area of the passage on one side ofthe central plane p-p of the draft tube than on the other, thusproviding for the increased flow on one side produced by the whirl, sothat this form will in some cases be preferable in providing for thewhirling components of flow.

In draft tube 46 of Figs. 9 and 10 the curvature commences close to therunner discharge and the core 47 is installed close to the runner. Asindicated at lines 4.7 in Fig. 9, the core is carried all the way up tothe runner and merges with the runner hub. The surface 48 of the core iscarried down far enough to merge with the original floor 50 of the tube.In Fig. 10a section is shown taken on the line 10-1O of Fig. 9 andindicating by dotted lines 51 the extreme horizontal width of thepassage at various points. In Figs. 11 and 12 the draft tube 55 has astraight entrance portion 56 and a horizontal outlet passage 57 which isflat in section. The core 59 for this draft tube is located at Y theelbow portion and has its surface 60 extendin to the final outlet edgeof the passage thus providing an inclined floor 61 above the originalfloor 62 and extending across the passage as indicated in Fig. 12 whichis a section on the line 1212 of Fig. 11.

In Figs. 13 and 14 a draft tube is shown formed in accordance with thisinvention and involving a turning of the flow within an unsymmetricalannular space which is only slightly flared on the upstream side andlaterally. This embodiment of the invention is particularly advantageousin giving smooth and eflicient flow lines while keeping the overallwidth within a narrow lateral space so as to permit a close s acing of aseries of draft tubes in a power ouse foundation. In the tube of thesefigures the entrance portion 65 is straight with a limited flare 66 atthe lower end. This flare may all around or may be increased on thedownstream side at 6.6. A core 67 is provided projecting into the flaredportion of the tube and having its base portion 68 on the upstream sideconnected to n the flared portion of the tube by surface 69 which mayfor instance be semi-circular or approximately so around a center 70eccentrically displaced downstream with relation to the axis of theentrance portion of the draft tube as shown in plan View in 14. Thissurface extends around the core 67 .and merges with the sides 71 of theoutlet 72 of the draft tube, which outlet has a top surface 78 and floor74. The spacing between the flare 66, 66 and the surface of the core 67may be made the same all around or it may be increased on the downstreamside as compared with the upstream side. In the draft tube of thisinvention the surface 69 connects with the flaring portion 66 of thedraft tube before thisflare has completed its curve to from the axialdirection and thus the passage around the core 67 has a limited flare onthe upstream side and laterally while the flare 66 on the downstreamside is completed to substantially right angles to the axial to mergewith the top 73 of outlet 72. The flow will therefore be unsymmetricalaround the axis, a greater portion passing on the downstream side of thecentral core than passes on the upstream side. This construction gives alimited flare to the vertical portion of the draft tube reducing the lateral width of the passage around the core 67 and permitting closerspacing of the turbines in the powerhouse and a reduction in the widthof the cavity in the powerhouse substructure below the turbine.

The invention is not confined to the specific draft tubes shown but maybe applied to draft tubes of horizontal shaft turbines or various otherforms within the principles above set forth In some cases it may be desir-able to cut away an existing draft tube for the base of the cone orto provide anchorage rods 8 (Fig. 1) between the tube and the cone, itbeing understood that the principles of my invention are not onlyapplicableto the reconstruction of existing draft tubes but may beequally applied and embodied in newly built draft tubes. The result isthat a newly formed draft tube may be provided with a floor 39 which inlongitudinal section such as shown in Fig. 8 would be composed ofsubstantially straight line elements along the major portion of itslength while in trans verse section, which is usually considered as eingnormal to the direction of flow, the surface 39 would be higher at onepoint than at another such as shown in Fig. 6, thus presenting a ridgedisposed longitudinally along, preferably, the central axis of theoutlet 3.8 and extending to the terminus of outlet 38 to which point theridge is substantially fully maintained. It is also to be noted that inFig. 6 the ridge immediately below nu meral 38 is specifically shown ofconvex formation in opposed relation to the roof which is hereinspecifically shown of concave formation, although it is of course parentthat other specific formations and arrangements might be employed whilemain t-aining the principles of the invention and without departing fromthe spirit of the in vention as set forth in the appended claims.

I claim 1. A hydraulic draft tube having a central core concave awayfrom the turbine axis in sections containing said axis, and an outerreadily apsurface unequally spaced from said core (35 tube downstreamfrom said turbine, and flaring outward to a less extent on the sideupstream from the turbine axis.

2. A draft tube having a central core projeoting upward toward therunner from the bottom of said tube and. an outer surface curvingsubstantially from vertical to horizontal on the downstream side of thedraft tube and curving to a less extent and not attaining a horizontaldir ction on the upstream side of the draft tube.

3. A draft tube comprising for at least a portion of its length anannular passage of greater cross section onone side than on the other.

A. The combination with an elbow type draft tube, of an auxiliary corein the curved portion of said draft tube forming an annular passage ofgreater cross section on one side than on the other.

5. The combination with a draft tube of the elbow type, of a core in thecurved portion of said draft tube projecting upward from the outersurface of the elbow to lower the rate of increase in area so as toavoid obstruction and more efficiently convert velocity head intopressure head.

6. A draft tube comprising for at least a portion of its length anannular passage of greater cross-section on one side than on the otherand having means providing a spiral surface in said tube.

7 The combination with an elbow-type draft tube, of a core in the curvedportion thereof forming an annular passage of greater cross-section onone side than on the other, and at least a portion of said core having aspiral surface.

S. A draft tube comprising an axially ex tendin straight portion adaptedto decelerate the flow, a deflecting portion of generally elbowformation turning the flow from axial to radial while simultaneouslydecelerating it and comprising a bottom deflecting surface and spreadingside walls, a radial discharge passage receiving and decelerating theradially directed flow and having its width at least twice its height,and means forming a spiral surface in said draft tube.

9. A draft tube of generally elbow formation having a bend. for turningthe flow from an axial portion to a radial portion, the upstream surfaceof the elbow bend lying substantially entirely on the downstream side ofthe upstream surface of said axial portion, and means forming a spiralsurface in said tube.

10. A draft tube comprising an axially extending straight portionadapted to decelerate the flow, a deflecting portion of generally elbowformation turning the flow from axial to radial while simultaneouslydecelerating it, and a horizontal portion also adapted to decelerate theflow, and said elbow formation being so proportioned that the rate ofincrease of the cross sectional area of the draft tube is lowered whenpassing around said elbow formation and is subsequently in creased inthe horizontal portion.

11. A draft tube of generally elbow formation comprising inlet andoutlet portions, said outlet portion when out by a transverse planesubstantially normal to the flow presenting a surface curved to providea ridge of greater length than its greatest width.

12. A draft tube of generally elbow formation comprising inlet andoutlet portions, said outlet portion when out by atransverse planesubstantially normal to the flow presenting a convex surface disposed soas to provide a ridge of greater length than its greatest width andextending in a clownstream direction tothe terminus of said outlet; i

18. A draft tube of generally elbow formation comprising inlet andoutlet portions, said outlet portion having floor and roof surfaces, oneof which when out by planes normal to the flow being convex to provide aridge and the other surface being concave.

l t. A draft tube of generally elbow formation comprising inlet andoutlet portions, said outlet portion when out by a transverse planesubstantially normal to the flow presenting a ridge disposed centrallyand extending longitudinally of said outlet portion, said ridge in thedirection of flow having substantially straight lines for the majorportion of its length.

15. A draft tube of generally elbow formation comprising inlet andoutlet portions, saidontlet portion having a ridge between its sidesextending longitudinally to the terminus of said outlet to which pointthe ridge is substantially fully maintained.

16. A draft tube of generally elbow formation comprising inlet andoutlet portions, said outlet portion having a floor provided with alongitudinally extending ridge.

1?. A draft tube of generally elbow formation comprising inlet andoutlet portions, saidv outlet portion having a floor provided with alongitudinally extending ridge disposed along the center axis of thefloor.

18. A draft tube of generally elbow formation com risin inlet and outletportions said outlet portion having a floor provided with alongitudinally extending ridge disposed along the center axis of thefloor, said ridge in longitudinal section having substantially astraight line for the major portion of its length and extending to theterminus of the outlet.

HARVEY BIROHARD TAYLOR.

